There are some things to do within the page being linked which help Facebook find images in the first place. I was not having that problem. It was letting me pick the thumbnail but then not displaying it.

I noticed over time that the thumbnails eventually showed up. It seems as if it was a temporary glitch. I was removing and posting the links a couple of times so that may have messed it up a bit. But it seems to be working fine for me now. The best thing to do is nothing. Check back in a week or two, and then they eventually show up again.

I found out that this is an intermittent problem with Facebook. It seems to not work from time to time. The only thing to do is to try and post it a 2nd time. If it doesn't work the 2nd time, wait a day or two and then try it again.

The other day, I had the same problem and then doing to anything. The next day, when I looked at, the image I upload displayed. So, it looks like, in this case, that it uploaded the picture, but just couldn't display it right away.

My problem is similar but not the same. I have a page of motor and cars , and is supposed to be a wordpress modification, but when I post a link it never give me chance to add any image from the posts. While other blogs do. I try here coches.com.

I had exactly the same problem. Once I post a link, I don't get the thumbnail showed.
I found out that Facebook doesn't find the image into your server's directory when there are spaces in the image's name.

For example if this is the path to your image: "/your_server_directory/images/image name.jpg" it wouldn't pick it. You will have to remove the spaces from the image name - you should rename it to something like: "/your_server_directory/images/image_name.jpg" or "/your_server_directory/images/imagename.jpg" and after that it works like a charm!!